Graphic closure indicator for cockpit traffic display

ABSTRACT

A system for graphically displaying on a cockpit display an indication of closure (i.e. a “closure indictor”) with a selected target aircraft. In a preferred embodiment of the invention, the system only displays a closure indicator if: (1) the selected target aircraft is within a pre-determined monitoring zone; and (2) the track of the selected target aircraft is within a pre-determined variation angle of the track of the Own Ship aircraft. If the rate of closure between the selected target aircraft and the Own Ship aircraft is within a predetermined range of values, the closure indicator includes a closing/receding indicia (such as an upwardly or downwardly directed arrow) that indicates whether the Own Ship aircraft is closing in on or receding from the selected target aircraft. The system preferably removes the closure indicator from display when the Own Ship aircraft or the selected target aircraft ceases to be airborne.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/243,239, filed Oct. 25, 2000.

TECHNICAL FIELD

This invention relates to displays of traffic in the cockpit of anaircraft and, more particularly, relates to displaying an indication ofclosure between an Own Ship aircraft and a selected target aircraft inresponse to the flight characteristics of the selected target aircraftsatisfying certain specified criteria.

BACKGROUND OF THE INVENTION

A primary task for pilots is to be aware of nearby air traffic bymaintaining a constant visual scan. If traffic is sighted, the pilotmust first assess the threat posed by the intruder aircraft, then, ifnecessary, maneuver to avoid the aircraft. This strategy is termed“see-and-avoid.” The effectiveness of see-and-avoid depends on theability of a pilot to visually acquire an intruder aircraft early enoughin the encounter to enable threat assessment and avoidance. A CockpitDisplay of Traffic Information (CDTI) assists the pilot withsee-and-avoid by providing a display of nearby traffic.

A CDTI display typically displays nearby target aircraft and informationabout the target aircraft, such as altitude, track, and identificationinformation. This information may be received from one or more sources,including Traffic Information Service (TIS) from a ground-based airtraffic control center, and Automatic Dependent Surveillance-Broadcast(ADS-B) from transponders on other aircraft, or vehicles.

The ability to easily determine from the display the movement of nearbyaircraft relative to the aircraft containing the display is especiallydesirable for effective threat assessment and avoidance. Additionally,aircraft operations can benefit from the timely and effectivepresentation of traffic information that can assist in decision makingfor the flight crew. Thus, there is a need for enhancements to CDTIunits to provide easily-readable graphic indications of the relativemovement and status of nearby aircraft.

SUMMARY OF THE INVENTION

The present invention is an improvement in displaying trafficinformation on an aircraft display, such as a CDTI. More specifically,the invention provides a method and system for graphically displaying ona cockpit display a graphical indication of the rate at which an OwnShip aircraft is closing in on, or receding from, a selected targetaircraft. This rate, which is generally referred to as a “closure rate”,has a positive value if the Own Ship aircraft is closing in on theselected target aircraft, and a negative value if the Own Ship aircraftis receding from the selected target aircraft. The graphical indicationof the rate at which the Own Ship aircraft is closing in on, or recedingfrom, the selected target aircraft is generally referred to as a“closure indicator.”

In a preferred embodiment of the invention, the system displays aclosure indicator in response, at least in part, to both of thefollowing requirements being satisfied: (1) the selected target aircraftis within a pre-determined monitoring zone; and (2) the track of theselected target aircraft is within a pre-determined variation angle ofthe track of the Own Ship aircraft. In an alternative embodiment of theinvention, the system also displays the closure indicator, at least inpart, in response to (3) the rate of closure between the selected targetaircraft and the Own Ship aircraft being within a predetermined range ofvalues. In a preferred embodiment of the invention, the system isconfigured to display no closure indicator, at least partially inresponse to the system failing to meet one or more of the aboverequirements.

As noted above, a system according to a preferred embodiment of theinvention only displays a closure indicator if the first two of theabove requirements are satisfied. However, in various alternativeembodiments of the invention, the system is configured to display aclosure indicator only if a different pre-determined two of the aboverequirements are satisfied. For example, in one embodiment of theinvention, the system only displays a closure indicator if requirements1 and 3, above, are satisfied. Such a system only displays a closureindicator if: (1) the selected target aircraft is within apre-determined monitoring zone; and (2) the rate of closure between theselected target aircraft and the Own Ship aircraft is within apredetermined range of values. In another embodiment of the invention,the system only displays a closure indicator if requirements 2 and 3,above, are satisfied. Such a system only displays a closure indicatorif: (1) the track of the selected target aircraft is within apre-determined variation angle of the track of the Own Ship aircraft,and (2) the rate of closure between the selected target aircraft and theOwn Ship aircraft is within a predetermined range of values.

In another alternative embodiment of the invention, the system onlydisplays a closure indicator if each of requirements 1-3 is satisfied.Such a system only displays a closure indicator if: (1) the selectedtarget aircraft is within a pre-determined monitoring zone; (2) thetrack of the selected target aircraft is within a pre-determinedvariation angle of the track of the Own Ship aircraft; and (3) the rateof closure between the selected target aircraft and the Own Shipaircraft is within a predetermined range of values.

In a further alternative embodiment of the invention, the systemdisplays a closure indicator if a pre-determined one of the aboverequirements is satisfied. In an additional alternative embodiment ofthe invention, the system constantly displays a closure indicator on thedisplay screen while the aircraft is in flight.

The system is preferably configured to remove a closure indicator fromdisplay on the display screen in response to either the Own Shipaircraft landing or the selected target aircraft landing.

In a preferred embodiment of the invention, the pre-determinedmonitoring zone referenced above is positioned adjacent to a frontportion of the Own Ship aircraft. This pre-determined monitoring zone ispreferably a substantially cone-shaped segment of airspace.Additionally, the cone-shaped segment of airspace is preferablypositioned so that the apex of the cone-shaped segment of airspace isadjacent a front portion of the Own Ship aircraft. Furthermore, thecone-shaped segment of airspace is preferably oriented so that the axisof the cone-shaped segment of airspace is substantially co-linear withthe track of the Own Ship aircraft. In one embodiment of the invention,the apex of the cone-shaped segment of airspace is immediately adjacenta front portion of the Own Ship aircraft and the axis of the cone-shapedsegment of airspace is oriented in substantially the same direction asthe track of the Own Ship aircraft. The vertex angle of the cone-shapedsegment of airspace is preferably about 40 degrees. In a preferredembodiment of the invention, the system is configured for allowing auser to at least partially modify at least one boundary of themonitoring zone.

Turning now to the requirement that the track of the selected targetaircraft be within a predetermined variation angle of the Own Shipaircraft's track, the predetermined variation angle is preferably about20 degrees. In a preferred embodiment of the invention, the system isconfigured to allow a pilot or other user to modify the predeterminedvariation angle to account for current flying conditions.

The closure indicator displayed by the system preferably comprises analphanumeric value indicating the current rate at which the Own Shipaircraft is closing in on, or receding from, the selected targetaircraft. The closure indicator also preferably includes a plus or minussign immediately adjacent to the alphanumeric value to indicate whetherthe Own Ship aircraft is closing in on, or receding from, the selectedtarget aircraft. The closure indicator preferably includes a plus signif the Own Ship aircraft is closing in on the selected target aircraft.Similarly, the closure indicator preferably includes a minus sign if theOwn Ship aircraft is receding from the selected target aircraft.

In a preferred embodiment of the invention, if the rate of closurebetween the selected target aircraft and the Own Ship aircraft is withina predetermined range of values, the closure indicator also comprises aclosing/receding indicia that further indicates whether the Own Shipaircraft is closing in on, or receding from, the selected targetaircraft. In a preferred embodiment of the invention, theclosing/receding indicia comprises an upwardly-directed arrow if the OwnShip aircraft is closing in on the selected target aircraft, and adownwardly-directed arrow if the Own Ship aircraft is receding from theselected target aircraft.

More particularly, the system is preferably configured to display, atleast in part in response to the closure rate being above apredetermined upper threshold value, a closure indicator that includes aclosing/receding indicia that indicates that the Own Ship aircraft isclosing in on the selected target aircraft. Similarly, the system isalso preferably configured to display, at least in part in response tothe closure rate being below a predetermined lower threshold value, aclosure indicator that includes a closing/receding indicia thatindicates that the Own Ship aircraft is receding from the selectedtarget aircraft. Furthermore, in this embodiment of the invention, thesystem is configured to display a closure indicator that includes noclosing/receding indicia if the closure rate is both: (1) equal to orabove the predetermined lower threshold value; and (2) equal to or belowthe predetermined upper threshold value.

In a preferred embodiment of the invention, if the closure rate is abovea predetermined upper threshold value, the system displays the closureindicator above a symbol representing the Own Ship aircraft. Similarly,if the closure rate is below a predetermined lower threshold value, thesystem displays the closure indicator below a symbol representing theOwn Ship aircraft. In this embodiment of the invention, the system isconfigured to display the closure indicator to one side of a symbolrepresenting the Own Ship aircraft if the closure rate is both: (1)equal to or above the predetermined lower threshold value; and (2) equalto or below the predetermined upper threshold value.

In a preferred embodiment of the invention, the predetermined upperthreshold value is about 5 knots and the predetermined lower thresholdvalue is about −5 knots. The system is preferably configured to allow auser to modify either the predetermined upper threshold value, thepredetermined lower threshold value, or both the predetermined upperthreshold value and the predetermined lower threshold value toaccommodate current flying conditions.

In an alternative embodiment of the invention, the system is configuredto only display a rate of closure on the display screen if the rate ofclosure between the selected target aircraft and the Own Ship aircraftis within a predetermined range of values. In this embodiment of theinvention, the system is configured to display a closure indicator inresponse, at least in part, to the closure rate being above apredetermined upper threshold value. Furthermore, the system is alsopreferably configured to display a closure indicator in response, atleast in part, to the closure rate being below a predetermined lowerthreshold value. In this embodiment of the invention, the system isfurther configured to display no closure indicator on the system'sdisplay screen if the closure rate is both: (1) equal to or above thepredetermined lower threshold value; and (2) equal to or below thepredetermined upper threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a block diagram of an aircraft surveillance system accordingto a preferred embodiment of the invention.

FIG. 2 is a pictorial view of a CDTI display showing a closure indicatorthat is displayed by an aircraft surveillance system according to apreferred embodiment of the invention when the Own Ship aircraft isclosing in on a selected target aircraft at a rate of 40 knots.

FIG. 3 is a pictorial view of a CDTI display showing a closure indicatorthat is displayed by an aircraft surveillance system according to apreferred embodiment of the invention when the Own Ship aircraft isreceding from a selected target aircraft at a rate of 60 knots.

FIG. 4 is a pictorial view of a CDTI display showing a closure indicatorthat is displayed by an aircraft surveillance system according to apreferred embodiment of the invention when the Own Ship aircraft isreceding from a selected target aircraft at a rate of 4 knots.

FIG. 5 is a pictorial view of a keypad used in an aircraft surveillancesystem according to a preferred embodiment of the invention.

FIG. 6 is a graphically depicted top view of a monitoring zone accordingto a preferred embodiment of the invention in an example in which thereis no wind so that the heading and track of the Own Ship aircraft arethe same.

FIG. 7 is a graphical depiction of an example in which a systemaccording to a preferred embodiment of the invention only displays aclosure indicator on the CDTI display screen if the selected targetaircraft's track is within a variation of 20 degrees of the Own Shipaircraft's track.

FIGS. 8A and 8B depict a flowchart that generally describes the logicaloperation of a closure indicator display module according to the currentinvention.

FIG. 9 is a graphical depiction that is useful in demonstrating themethod used by the system to determine, based on the track and positionof a currently-selected target aircraft, whether to display a closureindicator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described in greater detail withreference to the accompanying drawings, which depict various preferredembodiments of the invention. Many modifications and other embodimentsof the invention will come to mind to an individual who is skilled inthe pertinent art as that individual reviews the description below andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed,and that modifications and other embodiments are intended to be includedwithin the scope of the invention. Although specific terms are employedin this description, they are used in a generic and descriptive senseonly and not for purposes of limitation. Like numbers refer to likeelements throughout.

As will be appreciated by one skilled in the art, the present inventionmay be embodied as a method, a data processing system, or a computerprogram product. Accordingly, the present invention may take the form ofan entirely hardware embodiment, an entirely software embodiment or anembodiment combining software and hardware aspects. Furthermore, thepresent invention may take the form of a computer program product on acomputer-readable storage medium having computer-readable program codemeans embodied in the storage medium. Any suitable computer-readablestorage medium may be utilized including hard disks, CD-ROMs, opticalstorage devices, or magnetic storage devices.

The present invention is described below with reference to blockdiagrams and flowchart illustrations of methods, apparatuses (i.e.,systems) and computer program products according to an embodiment of theinvention. It will be understood that each block of the block diagramsand flowchart illustrations, and combinations of blocks in the blockdiagrams and flowchart illustrations, respectively, can be implementedby computer program instructions. These computer program instructionsmay be loaded onto a general purpose computer, special purpose computer,or other programmable data processing apparatus to produce a machine,such that the instructions which execute on the computer or otherprogrammable data processing apparatus create means for implementing thefunctions specified in the flowchart block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instruction meansthat implement the function specified in the flowchart block or blocks.The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions that execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

Accordingly, blocks of the block diagrams and flowchart illustrationssupport combinations of means for performing the specified functions,combinations of steps for performing the specified functions and programinstruction means for performing the specified functions. It will alsobe understood that each block of the block diagrams and flowchartillustrations, and combinations of blocks in the block diagrams andflowchart illustrations, can be implemented by special purposehardware-based computer systems that perform the specified functions orsteps, or combinations of special purpose hardware and computerinstructions.

I. System Architecture

FIG. 1 shows a block diagram of an exemplary embodiment of an aircraftsurveillance system 50 according to a preferred embodiment of theinvention. As will be understood by one skilled in the relevanttechnical field, the aircraft surveillance system 50 is preferablyconfigured for use within the cockpit of the aircraft for which thesurveillance system is being used (i.e. the “Own Ship” aircraft).However, in alternative embodiments of the invention, the aircraftsurveillance system 50 may be configured to operate in a location thatis remote from the Own Ship aircraft. For example, the aircraftsurveillance system 50 may be positioned at a ground station, and may beconfigured to transmit information for display on a display screenwithin the cockpit of the Own Ship aircraft.

The aircraft surveillance system 50 includes a processor 60 thatcommunicates with other elements within the aircraft surveillance system50 via a system interface or bus 61. Also included in the aircraftsurveillance system 50 is a display device/input device 64 for receivingand displaying data. This display device/input device 64 may be, forexample, a keypad (such as the keypad 500 shown in FIG. 5) or pointingdevice that is used in combination with a display screen. The aircraftsurveillance system 50 further includes memory 66, which preferablyincludes both read only memory (ROM) 65 and random access memory (RAM)67. The server's ROM 65 is used to store a basic input/output system 26(BIOS), containing the basic routines that help to transfer informationbetween elements within the aircraft surveillance system 50.

In addition, the aircraft surveillance system 50 includes at least onestorage device 63, such as a hard disk drive, a floppy disk drive, aCD-ROM drive, or optical disk drive, for storing information on variouscomputer-readable media, such as a hard disk, a removable magnetic disk,or a CD-ROM disk. As will be appreciated by one of ordinary skill in theart, each of these storage devices 63 is connected to the system bus 61by an appropriate interface. The storage devices 63 and their associatedcomputer-readable media provide nonvolatile storage for the aircraftsurveillance system 50. It is important to note that thecomputer-readable media described above could be replaced by any othertype of computer-readable media known in the art. Such media include,for example, magnetic cassettes, flash memory cards, digital videodisks, and Bernoulli cartridges.

A number of program modules may be stored by the various storage devicesand within RAM 67. Such program modules include an operating system 80,and a closure indicator display module 100. The closure indicatordisplay module 100 controls certain aspects of the operation of theaircraft surveillance system 50, as is described in more detail below,with the assistance of the processor 60 and an operating system 80.

Also located within the aircraft surveillance system 50 is a systeminterface 74, for interfacing and communicating with other elements ofthe aircraft's navigational system. It will be appreciated by one ofordinary skill in the art that one or more of the aircraft surveillancesystem's components may be located geographically remotely from otheraircraft surveillance system 50 components. Furthermore, one or more ofthe components may be combined, and additional components performingfunctions described herein may be included in the aircraft surveillancesystem 50.

II. System Overview

A system according to a preferred embodiment of the present inventionincludes a CDTI display for graphically displaying traffic informationto a pilot within the cockpit of an aircraft. FIGS. 2, 3, and 4 arepictorial representations of such a CDTI display. As may be understoodfrom these figures, a typical CDTI display 200, 300, 400 includes agraphical depiction of an Own Ship aircraft 202, 302, 402 and variousaircraft (such as aircraft 205, 305, 405) that are flying in the generalvicinity of the Own Ship aircraft 202, 302, 402. Such aircraft aregenerally referred to as “target” aircraft 205, 305, 405. The CDTIfurther includes a keypad, such as the keypad 500 shown in FIG. 5, forallowing a pilot of the Own Ship aircraft 202, 302, 402 to changevarious display parameters on the CDTI display. This keypad 500preferably includes a TGT button 520 that is configured to allow a userto turn a “target selection mode” on or off. When the target selectionmode is turned on, the user may use the T↑ button 521 and the T↓ button522 to select a current target aircraft by toggling between the varioustarget aircraft 205, 305, 405. The T↑ button 521 selects, as the nextselected target aircraft, the next farthest target aircraft from the OwnShip aircraft 202, 302, 402. Similarly, the T↓ button 522, selects, asthe next selected target aircraft, the next nearest target aircraft fromthe Own Ship aircraft 202, 302, 402.

As shown in FIG. 2, once the pilot designates a particular aircraft asthe selected target aircraft, the system visually distinguishes theselected aircraft 205 from other target aircraft by displaying a thinline 207 around the outer perimeter of the symbol representing theselected target aircraft 205, and by changing the color of the symbolrepresenting the selected target aircraft 205. The system alsopreferably displays additional information regarding the selected targetaircraft 205. For example, as shown in FIG. 2, the system displays theground speed 215 of the selected target aircraft in the lower left handcorner of the CDTI display screen 200.

The present invention provides an enhanced CDTI display that alertspilots to changes in the relative positions, tracks, and movement of theOwn Ship aircraft 202, 302, 402 and the selected target aircraft 205,305, 405. In a preferred embodiment of the invention, when the relativepositions, tracks, and rates of closure of the Own Ship aircraft 202,302, 402 and the selected target aircraft 205, 305, 405 meet certainconditions, the system displays, in an easily-readable, graphicalmanner, an indication of closure 220, 320, 420 between the Own Shipaircraft 202, 302, 402 and the selected target aircraft 205, 305, 405. Agraphic closure indicator according to a preferred embodiment of theinvention is described in greater detail below.

III. Display of Closure Indicator

In a preferred embodiment of the invention, the system is configured todisplay a closure indicator 220, 320, 420 on the display screen 200,300, 400 of an aircraft surveillance system (such as a CDTI) whencertain conditions are satisfied. As may be understood from FIGS. 2 and3, the system preferably displays the closure indicator 220, 320, 420adjacent a symbol that represents the Own Ship aircraft 202, 302, 402.

In a preferred embodiment of the invention, the closure indicator 220,320, 420 includes a closure rate indicator 224, 324, 424 that indicatesthe current rate at which the Own Ship aircraft 202, 302, 402 is closingin on, or receding from, the selected target aircraft 205, 305, 405.This closure rate indicator 224, 324, 424 preferably comprises analphanumeric closure rate value 226, 326, 426 and a positive or negativesymbol 228, 328, 428 to indicate whether the Own Ship aircraft 202, 302,402 is closing in on, or receding from, the selected target aircraft205, 305, 405. In this embodiment of the invention, the closure rateindicator 224, 324, 424 includes a positive sign immediately to the leftof the alphanumeric closure rate value 226, 326, 426 if the Own Shipaircraft 202, 302 is closing in on the selected target aircraft 205,305, 405. By the same token, the closure rate indicator 224 includes anegative sign immediately to the left of the alphanumeric closure ratevalue 226, 326, 426 if the Own Ship aircraft 202, 302, 402 is recedingfrom the selected target aircraft 205, 305, 405. In a preferredembodiment of the invention, the closure rate indicator 224, 324, 424displays the closure rate in knots.

In a preferred embodiment of the invention, the closure indicator 220,320, 420 may also comprise a closing/receding indicia 222, 322 thatfurther indicates whether the Own Ship aircraft 202, 302, 402 is closingin on, or receding from, the selected target aircraft 205, 305, 405.This closing/receding indicia 222, 322 is preferably a directionalsymbol that indicates by its orientation whether the Own Ship aircraft202, 302, 402 is closing in on, or receding from, the selected targetaircraft 205, 305, 405. In a preferred embodiment of the invention, theclosing/receding indicia 222, 322 is displayed (as shown in FIG. 2) asan upwardly-directed arrow if the Own Ship aircraft 202, 302, 402 isclosing in on the selected target aircraft 205, 305, 405. Similarly, inthis embodiment of the invention, the closing/receding indicia 222, 322is displayed as a downwardly-directed arrow (as shown in FIG. 3) if theOwn Ship aircraft 202, 302, 402 is receding from the selected targetaircraft 205, 305, 405.

The system is preferably configured so that the closure indicator 220,320, 420 only includes a closing/receding indicia 222, 322 if the rateof closure between the Own Ship aircraft 202, 302, 402 and the selectedtarget aircraft 205, 305, 405 is within a pre-determined range. In apreferred embodiment of the invention, the closure indicator 220, 320,420 only includes a closing/receding indicia 222, 322 if the rate ofclosure between the Own Ship aircraft 202, 302, 402 and the selectedtarget aircraft 205, 305, 405 is: (1) greater than a pre-determinedupper threshold value; or (2) less than a pre-determined lower thresholdvalue. Otherwise, as shown in FIG. 4, the system preferably displays aclosure indicator 220, 320, 420 that does not include a closing/recedingindicia 222, 322. In a preferred embodiment of the invention, thepre-determined upper threshold value is 5 knots, and the pre-determinedlower threshold value is −5 knots.

It should be understood that the pre-determined range (or ranges) ofclosure rates for which the closure indicator 220, 330 will include aclosing/receding indicia 222, 322 can be defined according to anydesired set of display rules. For example, the system may be configuredso that the closure indicator 220, 330 will only include aclosing/receding indicia 222, 322 if the current rate of closure betweenthe Own Ship aircraft 202, 302, 402 and the selected target aircraft205, 305, 405 is greater than a pre-determined upper threshold value.Alternatively, the system may be configured so that the closureindicator 220, 330 will only include a closing/receding indicia 222, 322if the current rate of closure between the Own Ship aircraft 202, 302,402 and the selected target aircraft 205, 305, 405 is less than apre-determined lower threshold value. In an alternative embodiment ofthe invention, the system may be configured so that the closureindicator 220, 330 always includes a closing/receding indicia 222, 322.

In a preferred embodiment of the invention, the system is configured toallow a pilot, or other user, to define (preferably while the aircraftis in flight) the pre-determined range (or ranges) of closure rates forwhich the closure indicator 220, 330 will include a closing/recedingindicia 222, 322. For example, the system may allow a pilot or otheruser to modify the pre-determined upper threshold value and/or thepre-determined lower threshold value as desired. This feature isadvantageous because it allows a pilot to set the pre-determined rangefor closing/receding indicia display in response to current flyingconditions.

To enhance the readability of the display screen 200, 300, 400, thesystem is preferably configured to position the closure indicator 220,320, 420 on the display screen 200, 300, 400 in response to the closurerate between the Own Ship aircraft 202, 302, 402 and the selected targetaircraft 205, 305, 405 satisfying certain criteria. For example, in apreferred embodiment of the invention, the system is configured todisplay the closure indicator 220, 320, 420 immediately adjacent thefront end 203, 303 of the symbol representing the Own Ship aircraft 202,302, 402 (as shown in FIG. 2) if the rate of closure between the OwnShip aircraft 202, 302, 402 and the selected target aircraft 205, 305,405 is greater than the pre-determined upper threshold value. In thisembodiment of the invention, the system is further configured to displaythe closure indicator 220, 320, 420 immediately adjacent the rear end204, 304 of the Own Ship symbol 202, 302, 402 (as shown in FIG. 3) ifthe rate of closure between the Own Ship aircraft 202, 302, 402 and theselected target aircraft 205, 305, 405 is less than the predeterminedlower threshold value. The system is further preferably configured todisplay the closure indicator 220, 320 to one side of a symbolrepresenting the Own Ship aircraft 202, 302, 402 (as shown in FIG. 4) ifthe closure rate is both: (1) equal to or above the predetermined lowerthreshold value; and (2) equal to or below the predetermined upperthreshold value.

FIGS. 2, 3, and 4 provide two examples of closure indicators 220, 320,420 according to a preferred embodiment of the invention. FIG. 2 depictsa situation in which an Own Ship aircraft 202 is closing in on theselected target aircraft 205, at a rate of 40 knots. As shown in thisfigure, because the Own Ship aircraft 202 is closing in on the selectedtarget aircraft 205, the closure indicator 220 includes a plus sign 228immediately to the left of the closure rate indicator 226. Furthermore,because the Own Ship aircraft 202 is closing in on the selected targetaircraft 205 at a rate that is greater than a predetermined upperthreshold value of 5 knots, the closure indicator 220 includes anupwardly-directed arrow 222 and the closure indicator 220 is positionedimmediately adjacent a front end 203 of the symbol representing the OwnShip aircraft 202.

FIG. 3 depicts a situation in which an Own Ship aircraft 302 is recedingfrom the selected target aircraft 305 at a rate of 60 knots. As shown inthis figure, because the Own Ship aircraft 302 is receding from theselected target aircraft 305, the closure indicator 320 includes a minussign 328 immediately to the left of the closure rate indicator 326.Furthermore, because the Own Ship aircraft 302 is receding from theselected target aircraft 305 at a rate that is less than a predeterminedlower threshold value of −5 knots, the closure indicator 320 includes adownwardly-directed arrow 322 and the closure indicator 320 ispositioned immediately adjacent a rear end 303 of the symbolrepresenting the Own Ship aircraft 302.

FIG. 4 depicts a situation in which an Own Ship aircraft 402 is recedingfrom the selected target aircraft 405 at a rate of 4 knots. As shown inthis figure, because the Own Ship aircraft 402 is receding from theselected target aircraft 405, the closure indicator 420 includes a minussign 428 immediately to the left of the closure rate indicator 426.Furthermore, because the closure rate between the Own Ship aircraft 402and the selected target aircraft 405 is less than a predetermined upperthreshold value of 5 knots, and greater than a predetermined lowerthreshold value of −5 knots, the closure indicator 420 includes noclosing/receding indicia 222, 322 and the closure indicator 420 ispositioned to one side of the symbol representing the Own Ship aircraft402.

It should be understood that the preferred embodiment of the inventiondescribed above conveys, in three different ways, whether the Own Shipaircraft 202, 302, 402 is closing in on or receding from the selectedtarget aircraft 205, 305, 405. More particularly, the system conveysthis information via: (1) a plus or minus sign 228, 328, 428 displayedimmediately to the left of the alphanumeric closure rate value 226, 326,426; (2) the orientation of the closing/receding indicia 222, 322; and(3) the position of the closure indicator 220, 320 relative to the OwnShip symbol 202, 302, 402.

It should be understood that alternative embodiments of the inventionmay be configured to use any two of the above methods to indicate witherthe Own Ship aircraft is closing in on, or receding from, the selectedtarget aircraft. For example, the system may be configured to indicatewhether the Own Ship is closing in on, or receding from the selectedtarget aircraft by displaying a positive or negative sign 228, 328, 428immediately to the left of the alphanumeric closure rate value 226, 326,426, and by displaying a properly-oriented closing/receding indicia 222,322, but not by varying the position of the closure indicator 220, 320relative to the Own Ship symbol 202, 302, 402. Similarly, the system maybe configured to display a positive or negative sign 228, 328, 428immediately to the left of the alphanumeric closure rate value 226, 326,426 and to vary the position of the closure indicator 220, 320 relativeto the Own Ship symbol 202, 302, 402 according to whether the Own Shipaircraft is closing in on or receding from the selected target aircraft205, 305, 405, but not to include a closing/receding indicia 222, 322for indicating the relative movement of the Own Ship aircraft 202, 302,402 and the selected target aircraft 205, 305, 405.

By the same token, the system may be configured to display only one ofthe three indicators of closing/receding discussed above. For example,in an alternative embodiment of the invention, the system may beconfigured to vary the position of the closure indicator 320 relative tothe Own Ship symbol 202, 302, 402 according to whether the Own Shipaircraft 202, 302, 402 is closing in on or receding from the selectedtarget aircraft 205, 305, 405, but not to include a positive or negativesign 228, 328, 428 or a closing/receding indicia 222, 322 to indicatethe relative movement of the Own Ship aircraft 202, 302, 402 and theselected target aircraft 205, 305, 405.

IV. Conditions For Closure Indicator Display

As noted above, in a preferred embodiment of the invention, the systemonly displays the closure indicator 220, 320, 420 on the display screen200, 300, 400 under certain pre-determined conditions. Morespecifically, the system preferably only displays the closure indicator220, 320, 420 if: (1) the selected target aircraft 205, 305, 405 iswithin a pre-determined monitoring zone; and (2) the track of theselected target aircraft 205, 305, 405 is within a specified varianceangle of the track of the Own Ship aircraft 202, 302, 402. In analternative embodiment of the invention, the system will only display aclosure indicator 223, 320, 420 if the above two requirements aresatisfied and: (3) the closure rate between the Own Ship aircraft 202,302, 402 and the selected target aircraft 205, 305, 405 is within acertain pre-determined range. These conditions are discussed in greaterdetail below.

A. Requirement 1—The Selected Target Aircraft is within a Pre-DeterminedMonitoring Zone.

As noted above, the system preferably only displays a closure indicator220, 320, 420 on the display screen 200, 300, 400 if the selected targetaircraft 205, 305, 405 is within a pre-determined monitoring zone 604,904. In a preferred embodiment of the invention depicted in FIG. 6, thismonitoring zone 604 is a three-dimensional, substantially cone-shapedsegment of airspace having an axis 610 that is substantially co-linearwith the track 615 of the Own Ship aircraft 602. The apex 630 of thiscone is preferably immediately adjacent a front end 620 of the Own Shipaircraft 602 and extends outwardly from the front of the Own Shipaircraft 602. In a preferred embodiment of the invention, thecone-shaped segment of airspace is in the form of a right cone and thevertex angle 635 of the cone-shaped segment of airspace is about 40degrees. (Note: For the sake of simplifying FIGS. 6, 7, and 9, thesefigures each depict examples in which there is no wind so that the trackof the Own Ship aircraft 602, 702, 902 is the same as the heading of theOwn Ship aircraft 602, 702, 902, and so that the track of each targetaircraft is the same as its heading.)

As will be understood by one skilled in the art, while the monitoringzone 604 is preferably a cone-shaped segment of airspace extendingoutwardly from the front portion 620 of the Own Ship aircraft 602, themonitoring zone 604 can be in any other shape or orientation. Forexample, the monitoring zone 604 could be in the form of an elongatedcylinder that has a major axis that is substantially co-linear with themajor axis 615 of the Own Ship aircraft 602. Alternatively, themonitoring zone 604 could be in the form of a cone that is not a rightcone, or a right cone that has its apex adjacent the rear end 625 of theOwn Ship aircraft 602 rather than the front end 620 of the Own Shipaircraft 602. In a preferred embodiment of the invention, to accommodatecurrent flying conditions, the system is configured to allow a pilot orother user to select a current monitoring zone from several differentmonitoring zones having different shapes and orientations. In a furtherpreferred embodiment of the invention, the system is configured to allowa user to modify at least one boundary of the current monitoring zone604 as desired. For example, the system may allow a user to specify adifferent apex angle 635 for current a cone-shaped monitoring zone.This, in turn, would redefine the boundaries of the current monitoringzone 604.

B. Requirement 2—The Selected Target Aircraft's Track is within aSelected Variation Angle of the Own Ship Aircraft's Track

As noted above, the system preferably only displays a closure indicator220, 320, 420 on the CDTI display screen 200, 300, 400 if the selectedtarget aircraft's track is within a selected variation angle of the OwnShip aircraft's track. To determine the variation angle between theselected target aircraft's track and the track of the Own Ship aircraft202, 302, 402, the system first determines the two-dimensionalhorizontal track of the Own Ship aircraft 202, 302, 402. Next, thesystem determines the two-dimensional horizontal track of the selectedtarget aircraft 205, 305, 405. The system then determines a “variationangle” between the track of the Own Ship aircraft 202, 302, 402 and thetrack of the selected target aircraft 205, 305, 405. This variationangle is simply the angular difference between the track of the selectedtarget aircraft 205, 305, 405 and the track of the Own Ship aircraft202, 302, 402. If this angle is greater than a pre-determined thresholdvariation angle, the system does not display a closure indicator 220,320, 420 on the display screen 200, 300, 400.

FIG. 7 graphically illustrates an example in which there is no wind sothat the track of the Own Ship aircraft 702 is the same as the headingof the Own Ship aircraft 702, and so that the track of each targetaircraft is the same as its heading. In this example, the system onlydisplays a closure indicator 220, 320, 420 on the CDTI display screen200, 300, 400 if the selected target aircraft's track is within avariation angle of 20 degrees of the Own Ship aircraft's track. Moreparticularly, this figure depicts an Own Ship aircraft 702, a firstgroup of aircraft 705-730, 750-760 (“Group A”) that have tracks thatwould not result in a closure indicator 220, 320, 420 being displayed onthe Own Ship aircraft's display screen 200, 300, 400. This figure alsoincludes a second group of aircraft 735-745 (“Group B”) that have tracksthat would result in a closure indicator 220, 320, 420 being displayedon the Own Ship aircraft's display screen 200, 300, 400.

Turning to Group A, target aircraft 705, 710, 715, 720, 725, 730, 750,755, and 760 have tracks that are offset from the track of the Own Shipaircraft 702 in a clockwise direction by 25 degrees, 90 degrees, 155degrees, 205 degrees, 270 degrees, 335 degrees, 165 degrees, 180degrees, and 195 degrees, respectively. Accordingly, the variation anglebetween the track of the Own Ship aircraft 702 and the tracks of targetaircraft 705 and 730 is 25 degrees. Similarly, the variation anglebetween the track of the Own Ship aircraft 702 and the tracks of targetaircraft 715, 720 is 155 degrees. By the same token, the variation anglebetween the track of the Own Ship aircraft 702 and the tracks of targetaircraft 710, 725 is 90 degrees. Also, the variation angle between thetrack of Own Ship aircraft 702 and the tracks of target aircraft 750 and760 is 165 degrees. The variation angle between the track of the OwnShip aircraft 702 and the track of target aircraft 755 is 180 degrees.Because, in this example, the system will only display a closureindicator 220, 320, 420 if the variation angle between the Own Shipaircraft 702 and the selected target aircraft is 20 degrees or less, thesystem will not display a closure indicator 220, 320, 420 if any of theaircraft in Group A (i.e. aircraft 705, 710, 715, 720, 725, 730, 750,755, 760) is designated as the selected target aircraft.

Focusing now on Group B, target aircraft 740, 745, 735 have tracks thatare offset from the track of the Own Ship aircraft 702 in a clockwisedirection by 0 degrees, 15 degrees, and 345 degrees, respectively.Accordingly, the variation angle between the track of the Own Shipaircraft 702 and the tracks of target aircraft 745 and 735 is 15degrees. Similarly, the variation angle between the track of the OwnShip aircraft 702 and the track of target aircraft 740 is 0 degrees.Because, in this example, the system will display a closure indicator220, 320, 420 if the selected target aircraft's track diverges from thetrack of the Own Ship aircraft by a threshold variation angle of 20degrees or less, the system will display a closure indicator 220, 320,420 if any of the aircraft in Group B is designated as the selectedtarget aircraft.

While, in a preferred embodiment of the invention, the thresholdvariation angle is 20 degrees, the system may be configured to have alarger or smaller variation angle. In a preferred embodiment of theinvention, the system is configured to allow a pilot or other user tomodify the variation angle during flight to accommodate current flyingconditions or user preferences.

C. Requirement 3—The Rate of Closure is within a Pre-Determined Range.

As noted above, in an alternative embodiment of the invention, thesystem preferably only displays a closure indicator 220, 320, 420 on theCDTI display screen 200, 300, 400 if the rate of closure between the OwnShip aircraft 202, 302, 402 and the selected target aircraft 205, 305,405 is within a pre-determined range. More specifically, in thisembodiment of the invention, the system only displays a closureindicator 220, 320, 420 if the rate of closure between the Own Shipaircraft 202, 302, 402 and the selected target aircraft 205, 305, 405 iseither: (1) greater than a pre-determined upper threshold value; or (2)less than a pre-determined lower threshold value. Otherwise, the systemdoes not display a closure indicator 220, 320, 420 on the Own ShipAircraft's display screen. As noted above, in a preferred embodiment ofthe invention, the pre-determined upper threshold value is 5 knots, andthe pre-determined lower threshold value is −5 knots.

It should be understood that the pre-determined range (or ranges) ofclosure rates for which the system will display a closure indicator 220,320, 420 can be defined according to any desired set of display rules.For example, the system may be set to only display a closure indicator220, 320, 420 if the current rate of closure between the Own Shipaircraft 202, 302, 402 and the selected target aircraft 205, 305, 405 isgreater than a pre-determined upper threshold value. Alternatively, thesystem may be set to only display a closure indicator 220, 320, 420 ifthe current rate of closure between the Own Ship aircraft 202, 302, 402and the selected target aircraft 205, 305, 405 is less than apre-determined lower threshold value. In a preferred embodiment of theinvention, the system is configured to allow a pilot or other userdefine (preferably while the aircraft is in flight) the pre-determinedrange (or ranges) of closure rates for which the system will display aclosure indicator 220, 320, 420. This feature is advantageous because itallows a pilot to set the pre-determined range for closure rate displayin response to current flying conditions.

V. Alternative Embodiment Requiring Different Combinations of the AboveRequirements for Closure Indicator Display

In a preferred embodiment of the invention, the system is configured todisplay a closure indicator 220, 320, 420 in response to Requirements 1and 2, above, being satisfied. However, alternative embodiments of theinvention may be configured to display a closure indicator 220, 320, 420in response to any pre-determined combination of two or more ofRequirements 1-3 being satisfied. For example, the system may beconfigured to display a closure indicator 220, 320, 420 only if: (1) theselected target aircraft 205, 305, 405 is within a pre-determinedmonitoring zone; (2) the selected target aircraft's track is within aselected variation angle of the Own Ship aircraft's track; and (3) therate of closure between the Own Ship aircraft 202, 302, 402 and theselected target aircraft 205, 305, 405 is within a pre-determined range.Alternatively, the system may be configured to display a closureindicator 220, 320, 420 only if the selected target aircraft 205, 305,405 is within a pre-determined monitoring zone, and the rate of closurebetween the Own Ship aircraft 202, 302, 402 and the selected targetaircraft 205, 305, 405 is within a pre-determined range. As a furtheralternative, the system may be configured to display a closure indicator220, 320, 420 only if the selected target aircraft's track is within aselected variation angle of the Own Ship aircraft's track, and the rateof closure between the Own Ship aircraft 202, 302, 402 and the selectedtarget aircraft 205, 305, 405 is within a pre-determined range.

Furthermore, the system may be configured to display a closure indicator220, 320, 420 in response to only one of Requirements 1-3, above, beingsatisfied. For example, the system may be configured to display aclosure indicator 220, 320, 420 in response to the selected targetaircraft 205, 305, 405 being within a pre-determined monitoring zone.Similarly, the system may be configured to display a closure indicator220, 320, 420 in response to a track of the selected target aircraft205, 305, 405 being within a pre-determined variation angle of the trackof the Own Ship aircraft 202, 302, 402. By the same token, the systemmay be configured to display a closure indicator 220, 320, 420 inresponse to the rate of closure between the Own Ship aircraft 202, 302,402 and the selected target aircraft 205, 305, 405 being within apre-determined range. In a further embodiment of the invention, thesystem is configured to constantly display a closure indicator 220, 320,420 while the Own Ship aircraft 202, 302, 402 is in flight.

In a preferred embodiment of the invention, the system is configured toallow a pilot or other user to modify the conditions under which thesystem will display a closure indicator 220, 320, 420. The systempreferably allows this to be done while the aircraft is in flight. Forexample, in a preferred embodiment of the invention, the system mayallow a user to re-configure the system during flight from a firstconfiguration to a second configuration. In the first configuration, thesystem may be configured, for example, to display a closure indicator220, 320, 420 in response to the selected target aircraft's track beingwithin a selected variation angle of the Own Ship aircraft's track. Inthe second configuration, the system may be configured to display aclosure indicator 220, 320, 420 in response to: (1) the selected targetaircraft's track being within a selected variation angle of the Own Shipaircraft's track; and (2) the rate of closure between the Own Shipaircraft 202, 302, 402 and the selected target aircraft 205, 305, 405being within a pre-determined range. This functionality is advantageousbecause it allows pilots to configure the system as appropriate forcurrent flying conditions.

VI. Automatic Removal of the Closure Indicator from the Display Screen

In a preferred embodiment of the invention, the system removes a closureindicator 220, 320, 420 from display on the Own Ship aircraft's displayscreen 200, 300, 400 in response to the Own Ship aircraft 202, 302, 402landing. The system also preferably removes a closure indicator 220,320, 420 from display on the Own Ship Aircraft's display screen 200,300, 400 in response to the selected target aircraft 205, 305, 405landing. This functionality is useful because an indication of closureis no longer necessary once either the Own Ship aircraft 202, 302, 402or the selected target aircraft 205, 305, 405 has landed. In analternative embodiment of the invention, the system removes a closureindicator 220, 320, 420 from display on the Own Ship Aircraft's displayscreen 200, 300, 400 in response to the selected target aircraft 205,305, 405 landing, but does not move the closure indicator 220, 320, 420from display in response to the Own Ship aircraft 202, 302, 402 landing.In a further alternative embodiment of the invention, the system removesa closure indicator 220, 320, 420 from display on the Own Shipaircraft's display screen 200, 300, 400 in response to the Own Shipaircraft 202, 302, 402 landing, but does not move the closure indicator220, 320, 420 from display in response to the selected target aircraft205, 305, 405 landing.

VII. General Operation of a Preferred Embodiment of the Invention

FIGS. 8A and 8B depict the general logic flow of a closure indicatordisplay module 800 according to a preferred embodiment of the invention.When executing such a closure indicator display module 800, the systemfirst executes Step 810 in which the system determines whether theselected target aircraft 205, 305, 405 is within a pre-determinedmonitoring zone 604 as discussed above. If so, the system proceeds toStep 820. If not, the system proceeds to Step 825, does not display aclosure indicator 220, 320, 420 on the Own Ship aircraft's displayscreen 200, 300, 400, and returns to Step 810.

At Step 820, the system determines whether the selected targetaircraft's track is within a pre-determined variation angle of the OwnShip aircraft's track. If so, the system proceeds to Step 830. If not,the system proceeds to Step 825, does not display a closure indicator220, 320, 420 on the Own Ship aircraft's display screen 200, 300, 400,and returns to Step 810.

At Step 830, the system determines whether the closure rate between theselected target aircraft 205, 305, 405 and the Own Ship aircraft 202,302, 402 is equal to or below a pre-determined upper threshold value. Ifso, the system proceeds to Step 850. If not (i.e., the closure rate isabove the pre-determined upper threshold value), the system executesStep 840, where it displays a closure indicator 220, 320, 420 thatincludes a closing/receding indicia 222, 322. The system displays thisclosure indicator 220, 320 on the Own Ship aircraft's display screen200, 300, 400 immediately above a symbol representing the Own Shipaircraft 202, 302, 402. After executing Step 840, the system returns toStep 810.

At Step 850, the system determines whether the closure rate between theselected target aircraft 205, 305, 405 and the Own Ship aircraft 202,302, 402 is equal to or above a predetermined lower threshold value. Ifso, the system proceeds to Step 870, where it displays a closureindicator 220, 320, 420 that does not include a closing/recedingindicia. The system displays this closure indicator 220, 320 on the OwnShip aircraft's display screen 200, 300, 400 to one side of a symbolrepresenting the Own Ship aircraft 202, 302, 402. After executing Step870, the system returns to Step 810.

If the system determines, at Step 850, that the closure rate between theselected target aircraft 205, 305, 405 and the Own Ship aircraft 202,302, 402 is not equal to or above a predetermined lower threshold value(i.e., the closure rate is below the predetermined lower thresholdvalue), the system executes Step 860 where it displays a closureindicator 220, 320, 420 that includes a closing/receding indicia 222,322. The system displays this closure indicator 220, 320 on the Own Shipaircraft's display screen 200, 300, 400 immediately below a symbolrepresenting the Own Ship aircraft 202, 302, 402. After executing Step840, the system returns to Step 810.

In this embodiment of the invention, the system also removes the closureindicator 220, 320, 420 from display on the Own Ship aircraft's displayscreen 200, 300, 400 when either the Own Ship aircraft 202, 302, 402 orthe selected target aircraft 205, 305, 405 lands.

FIG. 9, which graphically depicts an Own Ship aircraft 902 flying inrelation to several target aircraft 940-960, may be used to furtherunderstand the general functionality of a system according to apreferred embodiment of the invention. In this preferred embodiment ofthe invention, the system is configured to only display a closureindicator 220, 320, 420 if the selected target aircraft is within apre-determined monitoring zone 904 that is defined by a cone-shapedsegment of airspace having an apex angle 935 of 40 degrees, that has anapex 930 that is positioned immediately adjacent the front end 920 ofthe Own Ship aircraft 902, and that extends outwardly from the frontportion 920 of the Own Ship aircraft 902 so that the axis 910 of thecone-shaped segment of airspace is substantially co-linear with themajor axis of the Own Ship aircraft 902.

Furthermore, the system is configured to only display a closureindicator 220, 320, 420 on the Own Ship aircraft's display screen if thetrack of the selected target aircraft is within a 20 degree variationangle from the Own Ship aircraft's track. As mentioned above, thisfigure depicts an example in which there is no wind so that the track ofthe Own Ship aircraft 902 is the same as the heading of the Own Shipaircraft 902, and so that the track of each target aircraft is the sameas its heading.

In the example shown in FIG. 9, the system clearly would not display aclosure indicator 220, 320, 420 if aircraft 945 were the selected targetaircraft because aircraft 945 is well outside of the pre-determinedmonitoring zone 904. Similarly, even though aircraft 940, 950, and 955may be within the pre-determined monitoring zone 904, the system wouldnot display a closure indicator 220, 320, 420 if any of these aircraftwere designated as the selected target aircraft because the variationangle between the track of each of these aircraft and the Own Shipaircraft 902 is greater than the threshold 20 degree variation angle.More particularly, the variation angle between track of the Own Shipaircraft 902 and the track of target aircraft 955 is about 90 degrees.Similarly, the variation angle between the Own Ship aircraft between thetrack of the Own Ship aircraft 902 and the track of the target aircraft950 is about 180 degrees. By the same token, the variation angle betweenthe track of the Own Ship aircraft 902 and the track of target aircraft940 is about 45 degrees.

As may be understood from FIG. 9, the variation angle between the OwnShip aircraft 902 and target aircraft 960 is about 0 degrees. Thus,presuming that aircraft 960 is not outside of the pre-determinedmonitoring zone 904 by virtue of its altitude, the system would displaya closure indicator 220, 320, 420 on the Own Ship aircraft's displayscreen 200, 300, 400 if this aircraft were the selected target aircraft.

VIII. Conclusion

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1-53. (canceled)
 54. A computer-readable medium comprisingcomputer-executable instructions for performing the steps of comparing atrack of a target aircraft with a track of an Own Ship aircraft;determining whether said target aircraft is within a pre-determinedmonitoring zone; and responsive, at least in part, to the track of saidtarget aircraft being within said pre-determined monitoring zone, causea closure indicator to be displayed on a display screen; responsive toinput from a user, modifying at least one boundary of said monitoringzone; and removing said closure indicator in response to at least one ofsaid Own Ship aircraft landing and said target aircraft landing.
 55. Thecomputer-readable medium of claim 54 wherein to compare a track of atarget aircraft with a track of an Own Ship aircraft, saidcomputer-readable medium further comprises computer-executableinstructions for determining a closure rate between said target aircraftand said Own Ship.
 56. The computer-readable medium of claim 54 whereinto compare a track of a target aircraft with a track of an Own Shipaircraft, said computer-readable medium further comprisescomputer-executable instructions for determining whether a closure ratebetween said target aircraft and said Own Ship is at least one of abovea predetermined lower threshold value and below a predetermined upperthreshold value.
 57. The computer-readable medium of claim 54 wherein tocompare a track of a target aircraft with a track of an Own Shipaircraft, said computer-readable medium further comprisescomputer-executable instructions for determining whether said track ofsaid target aircraft is within a pre-determined variation angle of saidtrack of said Own Ship.
 58. The computer-readable medium of claim 57wherein said computer-readable medium further comprisescomputer-executable instructions for causing an upwardly-directed arrowto be displayed if said Own Ship is closing in on said target aircraft.59. The computer-readable medium of claim 57 wherein saidcomputer-readable medium further comprises computer-executableinstructions for causing a downwardly-directed arrow to be displayed ifsaid Own Ship is receding from said target aircraft.
 60. Thecomputer-readable medium of claim 57 wherein said computer-readablemedium further comprises computer-executable instructions for causing analphanumeric value to be displayed indicating the current rate at whichsaid Own Ship is closing in on, or receding from, said target aircraft.61. A method of displaying aeronautical information, said methodcomprising the steps of comparing a track of a target aircraft with atrack of an Own Ship aircraft; determining whether said target aircraftis within a pre-determined monitoring zone; and responsive, at least inpart, to the track of said target aircraft being within saidpre-determined monitoring zone, displaying a closure indicator on adisplay screen; modifying at least one boundary of said monitoring zone;and removing said closure indicator in response to at least one of saidOwn Ship aircraft landing and said target aircraft landing.
 62. Themethod of claim 61 further comprising the step of determining theclosure rate between said target aircraft and said Own Ship.
 63. Themethod of claim 61 further comprising the step of determining whethersaid track of said target aircraft is within a pre-determined variationangle of said track of said Own Ship.
 64. The method of claim 61 furthercomprising the steps of: determining whether the closure rate betweensaid target aircraft and said Own Ship is below a predetermined lowerthreshold value; and displaying a closure indicator in response to saidclosure rate being below said predetermined lower threshold value. 65.The method of claim 61 further comprising the steps of: determiningwhether the closure rate between said target aircraft and said Own Shipis above a predetermined upper threshold value; and displaying a closureindicator in response to said closure rate being above saidpredetermined upper threshold value.
 66. The method of claim 65 furthercomprising the steps of: determining whether the closure rate betweensaid target aircraft and said Own Ship is at below a predetermined lowerthreshold value; and displaying no closure indicator in response to saidclosure rate being above said predetermined lower threshold value andbelow said predetermined upper threshold value.
 67. A system fordisplaying aeronautical information, said system comprising a processorconfigured to: compare a track of a target aircraft with a track of anOwn Ship aircraft; determine whether said target aircraft is within apre-determined monitoring zone; and cause a closure indicator to bedisplayed on a display based at least in part to the track of saidtarget aircraft being within said pre-determined monitoring zone;responsive to input from a user, modify at least one boundary of saidmonitoring zone; and remove said closure indicator in response to atleast one of said Own Ship aircraft landing and said target aircraftlanding.
 68. The system of claim 61 wherein said processor is furtherconfigured to determine whether said track of said target aircraft iswithin a pre-determined variation angle of said track of said Own Ship.69. The system of claim 61 wherein said processor is further configuredto: determine whether the closure rate between said target aircraft andsaid Own Ship is below a predetermined lower threshold value; anddisplay a closure indicator in response to said closure rate being belowsaid predetermined lower threshold value.
 70. The system of claim 61wherein said processor is further configured to determine the closurerate between said target aircraft and said Own Ship.
 71. The system ofclaim 61 wherein said processor is further configured to: determinewhether the closure rate between said target aircraft and said Own Shipis above a predetermined upper threshold value; and display a closureindicator in response to said closure rate being above saidpredetermined upper threshold value.